Are we (humans) better or worse prepared to evolve than other animals?

I had a debate recently with an aquaintance about whether or not humans are ruining the evolutionary process. His point was that by having medicine, vaccinations, life support, surgery etc. that inferior people were being allowed to stay in the gene pool and pass on their poor immune systems/weak muscles/inferior organs etc. I, of course, agreed that medicine etc. is allowing people with weaker immune systems to breed and pass on their genes for poor immune systems on, but I didn't think it was ruining evolution. The point I made was that humans are following the same routine that most dominant animals do, but to an exagerated extent. Since humans don't have the harsh life that animals do, more people with traits that are traditionally considered inferior are allowed to survive, but that also allows more random mutations to occur. With an animal like a tiger, there's a specific type of tiger that works best in a specific environment, and so most tigers follow that formula, have some variation that helps them or die off. But with humans, we have life relatively easy, and the random variaitions that develop (I feel) will help us as a species when some major stuff goes down and kills a bunch of us.

Immunesystems work a lot with chance. I wonder if you can call most weak (although some are), they are mostely unlucky.

You cannot predict what kind of immune system will be required to be fit in the future. Pathogens, viruses etc evolve and change constantly.

In a way we are preparing ourselves well for evolution since we are creating a lot of genetic diversity at the moment and mixing it around. That could lead to new and interesting combinations.

Another question is if we need to 'evolve'? We seem quite well adapted.

I also think that the fear of losing the evolutionary race is due to a misunderstanding of evolution. There is no progress as such in evolution, and therefore also no recession. There is extinction, but this is also a natural part of evolution. It happened just as often as speciation.

Unless of course you are not interested in human evolution, but have a political agenda in mind. You want to change the human species for some political purposes. Because that is what is really behind all the rethoric behind eugenics.

You might as well argue that by eating a good diet that we are reducing our chance to evolve the capacity to survive on a bad diet. By developing guns we reduce our chance to evolve useful claws and fangs.

One of the things that seperates us from less successful species is our accelerated social evolution. The entire basis of humanity's success is development of social systems that aid in the survival of the so-called "inferior" individuals. Does that confound physical evolution? Yes, but remember, the most significant mechanism of physical evolution is the eradication of species.

Evolution doesn't work toward a goal, and you're confusing evolution with natural selection. Evolution is the process whereby a species becomes distinct from its ancestral species. Natural selection is the process where certain traits already existing in a species are passed on to future generations because they either confer a benefit or are neutral for survival, while those traits that are deleterious for survival do not get passed on to future generations. Natural selection is simply a response to selection pressures, any selection pressures, not something with a predetermined direction, or where traits are good or bad other than in the context of the current environment. Medicine simply changes the selection pressures. Ability to fight off a certain infection is no longer an important trait because we can provide medicine for it instead.

Usually, when the selection pressure for a particular trait is decreased (same thing could happen naturally if, for example, the predator of another species went extinct...the prey species would no longer have the predation pressure to contend with), you begin to see more variability in that trait. Selection pressure usually keeps certain variations of a trait to a minimum because those variations are unfavorable (i.e., white fur color in a mouse that lives on the forest floor among brown leaves), while others become more abundant because it allows better survival in that selective environment (i.e., white fur color in a mouse living in the arctic where the ground is usually snow covered). Without that pressure, the full spectrum of variation for that trait can be expressed and passed on because there is nothing to make any of those variants undesirable (i.e., brown or white mice living in the walls of someone's house). If that pressure returns again (i.e., the house is demolished and the mice end up back in the woods), those individuals who have inherited the less desirable of the traits will wind up back at the mercy of that pressure and that trait will become less abundant again.

Keep in mind that all these terms refer to the population level, not necessarily an individual level. Occassionally, an albino mouse will survive in the woods long enough to reproduce and those genes are not completely lost, even though, in general, being a white mouse in a brown environment makes one particularly vulnerable to getting spotted and eaten by a predator.

Also, remember that natural selection does not involve acquiring new characteristics to fit a situation (they really shouldn't teach history of science...i.e., Lamarckian theory...right along with the modern day form of the theory of natural selection, it really seems to leave a lot of people thinking inheritance of acquired characteristics really happens). In other words, if you have to get food from a tall tree, you're not suddenly going to grow taller to reach the food. The population as a whole will not suddenly gain genes for tallness. If all your other food sources are gone except what's in a tall tree, one of two things happens: 1) the species goes extinct or 2) an existing trait allows some individuals to reach the food in the tall tree, and only those individuals survive to pass on their genes...for example, maybe there is a range of short to tall people, and the tallest people can reach the tree, while the shortest will all die off. There will be a shift in the average height of the population toward taller if this happens. Or, perhaps some of the shorter individuals also are really good tree-climbers even though they never needed to try it out before. Then those who are good tree climbers will pass on their genes to future generations and the species will have more good climbers. Both could also happen, the tall people and the really short, but good climbers both survive. Maybe the medium-sized people don't survive...they neither can reach the tree from the ground, nor are they small and agile enough to climb the tree. In this case, interbreeding between the tall and short populations may cease because their medium sized offspring never survive. With lack of interbreeding between the tall people and the good climbers, the populations will gradually become more distinct from on another, until they reach a point when they no longer can be considered the same species (unless, of course, prior to becoming that distinct, a food source lower to the ground reappears and they can interbreed again and produce medium height offspring able to survive).

Every now and then I see a story in the news about a woman birthing a litter of four or five babies due to her having received medical treatment for infertility. When that type of story is in the news, it always occurs to me that if the percentage of women who need such treatment rises as the generations go by, we could potentially become a species which relies on the fertility drugs, and if some disaster strikes us and knocks us back to a low-tech world, so that we could no longer manufacture the drugs or do the surgery or what have you, then we will become extinct. I suppose I am piling one implausibility on top of another implausibility when I speculate this way.

Similar idle thought: what if breasts evolve entirely in the direction of esthetics, rather than mammary function? As long as we have the technology to manufacture infant formula, that would not be a problem...

Well, I joke with my friend who specializes in infertility treatment that they are creating their own job security by allowing continuing generations of infertile patients when there is a genetic association. However, this isn't completely true, and they are still a small percentage of the population. There are plenty of people who are fertile and continue to have babies the old-fashioned way, by accident. In terms of breast aesthetics and mammary function, no worry there. Aesthetics are in the eye of the beholder anyway, but large and small breasts alike are capable of producing plenty of milk for a baby. A small breasted-woman with implants to make her appear larger, still has the genes for small breasts. Infant formula is not as good as breast milk, babies on formula are fatter than breast-fed babies (not just bigger as in growing faster, but fatter) and are more susceptible to illness because they are not getting a supply of antibodies from their moms. There are times when formula is beneficial to have, such as if the mother requires treatment for an illness and gets medicine that can be passed through breast milk, then it's good to have the option to feed the baby formula. On the other hand, although the last time formula was popular, fathers were still not overly involved in taking care of babies, formula-feeding can permit a different shift in parental strategy where a mother can invest less maternal care while shifting more of that burden to the father. So does the development of easier to use breast pumps. But since men who don't stick around to help raise a baby are still pretty good at fathering plenty of them, I don't see any of this technology leading to a shift in selection of which men get to breed.

But since men who don't stick around to help raise a baby are still pretty good at fathering plenty of them... - Moonbear

Yet another musing of mine for some time has been that societies--such as ours here in the USA--which transfer wealth from taxpayers to unwed mothers, rewarding them for having babies they can't afford on their own, are playing with fire if the offsping of such mothers tend to make the same sort of choice when they grow up. It seems there will come some point of saturation where the number of responsible, working, taxpaying citizens is a small enough fraction of the overall population that they will no longer be able to carry the burden that was created by women who get a free ride by choosing to give sexual access to males who will not help to pay for the raising of their offspring.

ADDED NOTE: This is where Zero steps in and accuses me of spreading right-wing B.S.

The vast majority of humans live past breeding age. Although evolution never ceases, this would have a major impact as there aren't too many characteristics being weeded out. Things normally considered a survival disadvantage such as poor eyesight, asthma, diabetes, and others that would probably normally die out in primitive times, live to pass on their genes. Also if I'm not mistaken, people that are poorer and have less education breed more so than richer and more educated people. "Survival of the fittest" is a rule that's been severely altered for the human race due to technology, modern society, and arbitrary laws.

Your second sentence doesn't follow from your first one. The fact that many humans live beyond reproductive age doesn't mean in and of itself that there is a "failure" of weeding out. The older humans do consume resources that might have gone into increased reproduction, but there is evidence that older members of society, paricularly "grannies" help the community support itself and thus contribute to better nutrition, and thus healthier babies. Nothing in society is so simple that naive one parameter linear expections can be relied upon.

Another interpretation is that we have already evolved to be so successful of a species that these "minor" variations don't have any effect on our survival. The really deleterious traits have already disappeared. I don't know if this is the right interpretation, but it is an alternative view.

As selfAdjoint just said, since persons beyond reproductive age can affect the survivals of their respective groups, natural selection thereby can work on characteristics of persons beyond reproductive age (and particularly, propensity for longevity).

Could the actions of the older unreproductive generation have a negative effect on the reproductive success of the younger generation,

And could this effect be subject to natural selection?

(I don't have any answers.)

In the case you conjecture, evolution would ensure that individuals did not live long past their reproductive span, since it requires that oldsters convey negative fitness to the reproducing generation.

Since we have evidence of old people (as old as present day limits) even in ancient populations, the conjecture seems to be false.

In the case you conjecture, evolution would ensure that individuals did not live long past their reproductive span, since it requires that oldsters convey negative fitness to the reproducing generation.

Since we have evidence of old people (as old as present day limits) even in ancient populations, the conjecture seems to be false.

There also evidence in the biology of human. Your immune system goes down from your early mid-twenty and is probably at it lowest after 55 years old. Most cancer develop after the age of 50. The social evidence of older people does proove that evolution did not have an impact on selecting out aging people. These people migth have been lucky and made that far. What was the percentage of these people in their group? A large percentage of people that have pass reproductive age migth have an impact on the survival of the rest of the population. Therefore evolution reach an equilibirum so that elder would stay in a given population with a minimun effect on the rest of the population.

Also men probably had very little selection pressure because most did not make it pass their 30's and men have good reproductive capabilities late in life whereas older women were probably more subject to pressure and menopause evolved.

True, but only for the past 2 or 3 centuries (very short in evolutionary timescales). It remains to be seen if we can maintain that.

Although evolution never ceases, this would have a major impact as there aren't too many characteristics being weeded out. Things normally considered a survival disadvantage such as poor eyesight, asthma, diabetes, and others that would probably normally die out in primitive times, live to pass on their genes.

True, but perhaps it's just a shift in focus for natural selection. I would say that a significant/defining part of human nature is intelligence/tool making. That could be our unique niche in which we are now being tested by natural selection. It would seem that our main competition at the moment is ourselves and pathogens. Other physical selection pressures still exist, although muted as compared to the past, as you explained. (But I don't recall the asthmatic kid with thick glasses getting many dates in high school. ) Perhaps a diminished physical edge will lead to a downfall, perhaps not, but over-specialization is not an uncommon occurrance in evolutionary history. The other side of the coin is that perhaps increased mental/behavioral capabilities (technology, cooperation, etc) will increase our chance of survival. It's already been a boost to our population, range, longevity, fertility, etc.

Pardon me for butting in, but there have been old people in all societies we have record of. The low average life span in early societies was largely due to the enormous death rate of babies and children. Once you got to reproductive age you had a better chance of getting old. Women still had the risks of childbearing, but the majority survived this.

Afterthought. There may have been an evolutionary balance that favored early old age but not extreme old age. Through my inlaws I met many first generation Polish Americans, mostly from peasant backgrounds. They seemed to die in their early 70's, mostly from heart conditions. I remember attending the 75th birthday of one of them, who had had a (then new) triple bypass. He told me he was the first man in his extended family to live to that age.

Does the existence of menopause fit in with the logic of evolution? Do species other than humans (or maybe primates generally) undergo menopause?

What I am thinking is that if women were genetically built to last about X years before dieing, and if a child needs to be about Y years old before it can thrive without a mother, then maybe it makes sense for evolution to arrange for menopause to kick in at X - Y years of age. That way the final of the woman's children has a good chance of living on to adulthood. She doesn't waste resources on the last few children who were destined to die right after she died, the way she would if there was no menopause.

Pardon me for butting in, but there have been old people in all societies we have record of. The low average life span in early societies was largely due to the enormous death rate of babies and children. Once you got to reproductive age you had a better chance of getting old. Women still had the risks of childbearing, but the majority survived this.